In vivo measurements of airway geometry and their mechanical properties are of fundamental use in pulmonary physiology and of clinical use in the assessment of lung airway disease. Radiographic bronchograms can be tediously analyzed to obtain dimensions of airways. However, this proposal makes use of a rapid non-invasive technique, an acoustic impulse response from the airways, to obtain a measure of airway geometry. An acoustic pressure pulse is applied as a barely noticeable input at the airway opening. The reflected pressure wave is recorded in time, and analysis of this wave results in an estimation of the lung impedance between 100 and 10,000 Hz. These data are then analyzed using data inversion methods to obtain an estimation of the serial distribution of airway geometry. Results from the current grant indicate a close correlation between changes in airway cross-section determined radiographically and changes in the area-distance curves produced by this technique. The present proposal is thus to 1) apply the acoustic pulse response technique to measure changes in airway cross-section produced by pharmacological agents and mechanical intervention, 2) test this technique against direct measurements in order to assess its accuracy in estimation absolute cross-sectional area, and 3) to conduct studies using animal models of peripheral airways disease to determine if this technique is useful in detecting airways disease.